There have been numerous devices either proposed or used for reducing the aerodynamic drag on an articulated road vehicle such as a tractor and semi-trailer vehicle, to provide for a smoother less turbulent flow of air from the cab of the tractor to the body of the trailer and across the gap between the cab and trailer body. For example, U.S. Pats. No. 3,241,876, No. 3,348,873 and No. 3,695,673 disclose various types of shields or air flow diverters for mounting on the top wall or roof of the tractor cab. Other types of air deflectors or controllers are adapted to be mounted on the front portion of the trailer body, for example, as disclosed in U.S. Pat. No. 2,863,695 and No. 3,697,120. Another solution for streamlining a tractor-trailer vehicle is by the use of telescoping air shields such as disclosed in U.S. Pat. No. 3,711,146 and U.S. Pat. No. 2,737,411 discloses an inflatable streamlining envelope which is mounted on the rear of a truck body.
In the design of any device or apparatus for reducing the aerodynamic drag on a tractor-trailer vehicle, it is highly desirable to obtain a maximum decrease in aerodynamic drag while minimizing the additional weight which is added to the vehicle. Furthermore, the cost of the apparatus must be economical in reference to the decrease in fuel consumption which results from a reduction in the aerodynamic drag. It has also been found highly desirable to provide for streamlining the flow of air over and around a tractor-trailer vehicle in order to reduce the aerodynamic influence or sidewash of air on passing automobiles and other vehicles and thereby increase the safety in passing. The streamline flow also provides for greater stability and control of the tractor-trailer vehicle and for a reduction in the noise level of the air flow around and over the vehicle.
It is also well known that a crosswind flow of air within the gap between the tractor cab and the trailer body increases the aerodynamic drag due to the force of the wind against the entire front surface area of the trailer body. A more detailed discussion of the flow turbulence over and around a semi-truck is set forth in an article entitled "Truck Aerodynamics" and published by General Motors Corporation in SAE Transactions, Volume 70, 1962, pp. 297-308, and in an article entitled "Beat the Built-In Head" and published in the September, 1973 issue of Commercial Car Journal.